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July 5, 1960
|-|_ G, BELJERS ETAL
2,944,232
DEVICE COMPRISING A CAVITY RESONATOR
Filed April 19, 1954
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2,944,232
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Patented July 5, 1960
1
2
‘ the axis 3 and partly parallel thereto.
2,944,232
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Provided in the bottom of the resonator 1 is a ferro
DEVICE COMPRISING A ‘CAVITY RESONATOR
Hugo Gerrit Beljers, Kornelis Swier Run], and Anton
Eduard Pannenborg, Emmasingel, Eindhoven, Nether
magnetic body 4, preferably made of material having a
large depth of penetration for the high-frequency oscil
lation, for example, ferrite, which body is subject to the
‘ lands, assignors, by mesne assignments, to North Amer
‘ ‘ican Philips Company, Inc., New York, N.Y., a cor
'
poration of Delaware
Such mode of
oscillation is indicated by the symbol TEm.
.
action of a polarising magnetic ?eld H0 produced by a
magnet 5. Ifgdesired, the body 4 may be replaced by a
‘
tubular ferroinagneticybody 4’ provided concentrically
Filed Apr. 19, 1954, set. No. 424,134
.10 withthe axis of rotation 3 or combined with this body
(see Fig. 3), in which event comparatively small ?elds
Claims priority, application Netherlands Apr. 29, 1953 i i ' 1-10 are suf?cient.
Fig. 4 shows resonance curves of such a cavity resona
4 Claims. (Cl. 333-73)
tor for ditferent values of the polarising ?eld. The term
This invention‘ relates to devices comprising a cavity 15 “resonance curve” is to be understood here to mean the
amplitude of the high-frequency oscillation generatedin
resonator containing a ferromagnetic body‘which is sub
ject to the action of a polarising magnetic ?eld.
the resonator as a function of the frequency f with a con
-A device of this kind has previously been suggested
stant excitation oscillation at the coupling loop 2 and
for amplitude modulation of a high-frequency oscilla'
measured at dilferent values of the strength H of the
'
tion in the resonator by variation of the polarising ?eld, 20 polarising ?eld.
,1 .The curve a, which applies to a comparatively Weak
the amplitude modulation being based on the inner struc
tureof thematerial used for ‘the ferromagnetic body.
polarising ?eld, is similar to the resonance curve of a
bandpass ?lter coupled critically,’ the curves b and c,
In the device according to the invention variation in the
which correspond to increasing values of the ?eld strength
resonance curve of the resonator under the action of the
polarising ?eld is ‘obtained on the ground of quite dif-. 25 H0, being similar to those of bandpass ?lters coupled
.ferent causes by a particular choice of the. mode of oscil
lation, of the resonator.‘ Variation in the polarising ?eld
in this device likewise results in amplitude modulation
.1 of the highfrequency oscillation, but this, may be-,com~
overcriticlally.
i
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,
verse high-frequency oscillation in the cavity resonator
1 may be decomposed into two circularly-polarised com
ponents of opposite senses of rotation about the axis of
‘ pletely free from the phase modulationwhichwas still
noticeable in the device previously suggested, whilst fur
_
This behaviour may be explained as follows: The trans
i ; rotation 3.
Said components can build up themselves
thermore the modulating. process remains active for arbi
as independent oscillations in the resonator 1 only if the.
trarily high frequencies of the high-frequency oscillation
resonator has natural frequencies ‘which substantially co
incide inatyleast two different directions, for example,
at right angles to‘ one‘ another,;the plane ‘of which is
in the resonator.
‘
According to the invention, a cavity resonator is used
parallel. to. the electrical ?eld strength E, that is to say
if the ‘resonator has a cross-sectional area which is cir
cular or, for example, square in, shape. If, however, the
resonator would have, for example, a rectangular cross
section‘which thus corresponds to two di?erent natural
which is symmetrical across at least two. different diam
eters thereof, such as a cavity having a circular or square
cross-sectional‘shape, and _a ferromagnetic body within
this ‘cavity is magnetically polarized at a value so ‘as to
cause the‘cavity, when electrically excited for producing
40
frequencies of the resonator in two relatively perpendic
an‘, electrical transverse TE‘ mode of oscillation,‘ to have
two different resonance frequencies for the two circularly
ular directions,.the said decomposition into circularly
polarised components has no “real physical importance.
polarized components of the transversehoscillation; By
varying the strength“ of the magnetic polarization, the
frequency spacing between the two different resonance
frequencies can be varied.
,
i
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_ If the ?eld H0 is equal to ‘zero, the ferromagneticlbody
4 exerts the same influence upon the said two compo
. nents, resulting in a resonance curve corresponding to
accompanying drawing, given by way of example, in
that of a ‘single circuit. However, if the ?eld Ho diifers
from zero, the susceptibility and the propagation constant
of the body 4 become di?erent ‘for the two circularly
which
polarised oscillations, as is known, as a result of the
Fig. 1 is an axial section of a device according to the
invention.
Faraday eifect, so that the resonator also has different
resonance frequencies for the said two oscillations, from
In order that the invention may be readily carried into
eifect, it will now be described with reference to the
which ensues the group of characteristic lines shown in
Fig. 2 shows the variation of the electric ?eld strength
Fig. 4.
in the resonator with reference to a cross-section.
If a band-pass ?lter characteristic is desired having a
Fig. 3 shows a variant of the device of Fig. 1.
constant band-width, for example, of the character of the
Fig. 4 shows characteristics of resonance curves ob
curve a or b in Fig. 4, the magnet 5 may be in the form
of a permanent magnet, for example, of a small disc of
tained with such devices.
Fig. 5 shows in greater detail an embodiment which
ferroxdure (not shown) which is pressed against the
serves more particularly for amplitude modulation of a
high-frequency oscillation.
50
body 4. If, however, a variable band-width is desired,
the magnetic ?eld may be varied, for example, between
the values of the polarisation ?eld strength H0 corre
Referring now to Fig. 1, reference numeral 1 indicates
a cylindrical cavity resonator which is excited by way
sponding to the curves a and b in Fig. 4.
of a coupling loop 2 in transverse high-frequency oscil
If the frequency of the excitation oscillation at the
lation of a wavelength, for example, of the order of 1
65 coupling loop 2 coincides with the resonance frequency
cm., ‘that is to say that the electrical ?eld passes from
f0 of the resonator 1 with ferromagnetic body 4 non
‘ one half of the wall of the cylinder to the other half
polarised, the amplitude with which the oscillation is built
(see Fig. 2), so that the electrical ?eld-strength compo
up in the resonator 1 decreases if the strength Ho of the
nent E of the high-frequency oscillation is at right angles
polarisation ?eld increases and more particularly if the
to the MlS of rotation 3 of the cylindrical cavity, whereas 70 body 4 has the ?at shape shown in Fig. 1, the said ampli
tude is substantially linearly dependent upon the ?eld
the magnetic ?eld-strength component H, as may be seen
from Fig. 1, is found to extend partly at right angles to
strength H0. However, since the phases of the two
2,944,232
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3
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. .4.
circularly~polarised> oscillations are equal and of opposite
sign’ for the frequency in, the variation- in amplitude is
substantially not accompanied by variation in phase, so
effect at microwave frequencies being positioned with
said cavity, magnetic ?eld means for magnetically polar
izing said ferromagnetic body in a direction parallel to
the axis of 'said cavity, said‘ cavity having symmetrical
that the device is excellently suitable for high-frequency
Fig. 5 shows such-an amplitude modulator comprising‘
dimensions in at least two directions in a plane normal
to said axis, so that said resonator, device has at least
. a: resonator 1 having a'ferromagnetic body 4-and a mag
net. 5; similar ‘to-that shown ilTFlg; 1'. The resonator 1
two substantially equal natural frequencies of resonance
is coupled hy way of a» coupling hole 17 provided'conce'n
ducingwithin said cavity a transverse high frequencyv
amplitude modulation.
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tri'cally with’ the antis- 3 to a wave lineS', 9» of, for exam
corresponding to said two directions, and means for pro:
10
pilc,-. rectangular cross-section td-iwhich a high-frequency
oscillation‘having a» frequency-substantially equal to f0
' is‘suppliecl by a- wave genera-tor 10-, for example, a kly
stron generator, the resonator libri'nging about a more
or less strong re?ection of the said- oscillation as a func
said cavity, said magnetic polarization of said- ferro-_
magnetic body being su?icient to‘ cause said cavity reso
nator device to have two different simultaneous resonant
' -
said magnetic polarization to a value at which‘ the reso
nance characteristic curve of said cavity is that of a band
pass ?lter.
inthe line 8‘: and the oscillation passed to the line 9 are
amplitude.
v
y
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frequencies for the two ci'rcularlypolarized components _ .
of said transverse oscillation, and means for adjusting
tion of the ?eld H0, so that both the oscillation re?ected‘
modulated in
oscillation having an electric ?eldrnormal to the :axis of
‘
The described phenomena maybe found up to arbi
trarily: high frequencies’ corresponding to the natural fre~
4. A cavity resonator device comprising a cavity, a
20
qnency of'the resonator. However, ‘at lower frequencies,
for example, up to about 10,000; mc'./s., they may be
come? less distinct, since in this case ‘the resonator 1 is
also liable to be damped and de'tuned in accordance with‘
the strength‘ H}, of the polarisation ?eld as a result of the
inner structure of‘the- ferromagnetic material of the body
4. However, this effect is found to disappear if the satu
said‘ cavity, magnetic ?eld. means for magnetically polar
izing- said ferromagnetic body in a direction parallel to
the axis of said cavity-said cavity having synnnetricali
dimensions'in at least two‘ directions in a plane normal
to. said axis, so that said resonator device has at least
two ‘substantially equal natural‘ frequencies of resonance
corresponding to‘ said two directions, and means for pro
ration ma-rrnetisatione124s of the ferromagnetic material,
1nultiplied"by the gyromagnetic constant (‘:23 ms./s'/l
Gauss), remains smaller than the frequency of the'trans
verse high-frequency’ oscillation;
What is
claimed’ is:
>
ferromagnetic material which exhibits’the gyromagnetic
effect‘at microwave frequencies being positioned with
ducing within said cavity a transverse high frequency
30 oscillation- having an electric ?eld normal to the axis of
said cavity; said- magnetic polarization of said ferro~~
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magnetic-‘body being su?cient' to cause said cavity res- >_
a , v
"1?. A- cavity resonator device comprising a cavity, a
ferromagnetic material which exhibits the gyromagnetic
effect at- rnicrowa-ve frequencies being positionedwith
onator‘device to'have twodi?erent simultaneousresonant ‘ -
frequencies for the two- circularlyapolarized' components.
35 of saidtransverse oscillation; and means 'for adjusting.
said cavity, magnetic ?eld‘ means for magnetically polar
saidlmagnetic pol'arization'to Ia value at which the. reso?
'nance characteristic curve of said cavity'resonator has
izing sa-idfferromagnetic body in a direction parallel to
the- axis of said‘ cavity,’ said’ cavity having symmetrical;
two dilferent resonance peaks.
dimensions in at least two directions‘ in a plane normal
to» ‘said axis,‘ so that said‘ resonator device has ‘at least 40
two substantially equal; natural‘ frequencies of resonance
corresponding to said‘, two' directions; and means for pro
'
45
- magnetic body being su?icient to cause saidv cavity res
onator device to-have two di?erent simultaneous reso-~
nant frequencies for‘ the-“two circularly polarized‘ com
ponents' of said transverse oscillation.
' 2. A device‘ as claimed inclaim- 1, including, means for 50
varying the value of said‘ polarizing ?eld, thereby to
amplitude-modulate said high-frequency oscillation sub—
stantia-lly without causing phase-modulation thereof.
3. A cavity resonator device comprising a cavity, a
was deiiindt. _;__'___t_-__ July 14,1953’
2,784,378
of
saijd'cavity, said magnetic polarization‘ of' said ferro
‘UNITED :STATES PATENTS 7
2,645,758.
ducing within said cavity a transverse high- frequency
' u ation having an electric: ?eld normal‘ to the
References Cited in the'iiil'e of this patent
Yager __.___|'_l___
2,798,295
___,Mar. 5’, 1957,
V. Hogan ___'___'_7 _______ _v___ July 2, 1957
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FOREIGN rATnNTs ~
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674,874"
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OTHER, REFERENCES
‘7
“Applied Scienti?c Research”; Section B, vol. 3, pages
142-144.
.
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“Physica”; XIV, No. 10; February 1949; pages 629
641.
'
“Philips Technical Review”; vol. 11, No. ‘11; May 1950, '
ferromagnetic material which exhibits the’ gyromagnetic 55 pages 3 13-322‘.
I

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